I don't really agree with everything above. Maybe not all guys are able to shoot their cum, but nearly all of them are. Some guys can't because of a physical defect, but anyone can.
Two factors mentioned about are hydration and diet. Staying hydrated is self explanatory. Try and keep a diet that contains foods that promote semen production. Pineapple, watermelon, eggs, certain nuts, oranges. There are other I can't remember, but I have good luck with these. Also there are some supplements that seem to help at least with volume.
Also, kegels or PC flexes and improve your ability to shoot cum with some distance, at least in my experience. But an even bigger factor is delaying your orgasm when jerking off and ensuring that you only allow yourself to cum when you reach the apex of the sensation. I find when I do this I am able to shoot a load just like when I was a teenager. If I slip up and end up cumming when I'm not at the peak of the sensation I will tend to cum without the force I could. I might still shoot, but not with the strength I could shoot with.